1. Field of the Invention
The invention relates to motion vector estimation and detection of covered/uncovered image parts. The invention also relates to motion-compensated interpolation, and to a display apparatus comprising means for carrying out such a motion-compensated interpolation.
2. Description of the Related Art
The paper "Motion estimation method using the spatio-temporal characteristics of moving objects", presented at the International Workshop on HDTV, Los Angeles, October, 1996, by H. Sonehara et al., discloses a motion vector detection method which takes account of the spatio-temporal continuity of motion vectors and the local characteristics of pictures. Motion vector trajectories are traced to assess the spatio-temporal continuity of motion vectors. To remove erroneous motion vectors detected in the covered/uncovered background of the contour area of moving objects, motion vectors are estimated by means of a detection-area hierarchy and the correlation of luminance signals. It is necessary to identify, in two sequential fields, the area (covered and uncovered background area) in which the picture correlation becomes indeterminate. For this, a detection block is set in the current field and vectors are detected in relation to the next field. Then a detection block is set in the next field and vectors are detected in relation to the current field. In short, motion vectors are detected two-way.
European Patent Specification EP-B-0,535,066 discloses a method of assigning the appropriate one (if any) of a plurality of possible motion vectors to pixels of a video signal consisting of a series of pictures, the method comprising the steps of: a backwards assignment operation in which a first input picture is shifted by each of a plurality of possible vectors and compared to a second, succeeding picture to determine assignment errors for each vector at each pixel; a forward assignment operation in which the second picture is shifted by each of a plurality of possible vectors and compared to the first picture to determine assignment errors for each vector at each pixel; and using, for each pixel, the assignment errors determined in both forward assignment and backwards assignment operations to determine whether any of the vectors is appropriate for that pixel. The method may further comprise comparing the assignment errors for the forward and backwards assignment operations for a pixel to determine whether the pixel may relate to revealed or obscured background. This combined vector assignment flags regions of both revealed and obscured background as `no match` so that a fallback interpolation technique can be used. This fallback interpolation technique has not been described. In an alternative method, vectors from the instant of an input picture are converted to an output picture at a different instant in time by projecting the input vectors forward in time (allowing for their motion). Several problems are inherent in projecting vectors forward in time. While these problems are not insurmountable the technique of combined forward and backward assignment is simpler and therefore more attractive.